Natural Quartz Crystals Research Articles

Certain UV-luminescence centers in crystalline quartzes

Models of luminescence centers are proposed in a number of natural quartz crystals on the basis of ESR, optical absorption, thermoluminescence, and luminescence data; these centers are responsible for their radiation in the 335–380-nm band and hole trapping centers. Corresponding mechanisms for x-ray and thermally stimulated luminescence are also suggested.

UV excitation spectra of thermoluminescence in quartz

Thermoluminescence was excited at 300 K in natural quartz crystals by monochromatic ultraviolet radiation. The excitation spectra of the main glow peaks were measured in the spectral region 1150–2000 Å. A strong excitation maximum appeared for all measured glow peaks in the region of high absorbance on the long wavelength tail of a sharp reflectance peak at 1275 Å. Some glow peaks showed excitation maxima also at photon energies smaller than the absorption edge of the material. The dependence of the TL intensities on the dose of the exciting radiation was investigated for various glow peaks and excitation wavelengths. A sublinear dependence was recorded for some peaks by excitation at 1275 Å, while the same peaks showed a strictly linear dependence up to relatively high radiation doses, when excited at 1600 Å.

Growth defects in a quartz druse <a+c> dislocations

Growth defects have been studied by X-ray topography in two natural quartz crystals from a Brasilian druse. Different types of defects have been observed and they showed similar configuration in both samples. Dislocations are analyzed and discussed. In particular, `pyramidal' dislocations with (a +c) Burgers vectors have been characterized: these uncommon dislocations are analyzed in detail because even today they are believed to be nucleated only by deformation processes. The observations, taken as a whole, indicate that defects of crystals from a druse present distinctive characteristics.

A trapped-hole center causing rose coloration of natural quartz

Abstract In rose-colored natural quartz crystals two new hole centers were detected and analyzed by electron paramagnetic resonance (EPR). A hole center with characteristic doublet and sextet hyperfine structures was identified as an O− ion bridging between a substitutional aluminum and phosphorus atom each. This center slowly bleaches in UV light and can be enhanced by X-ray irradiation. It is most likely responsible for the rose coloration and also explains the repeatedly reported bleaching of “rose” quartz in daylight. Light-induced transfer of the hole in the PO4, not the AlO4 unit is assumed to cause this strong visible absorption. Several features of this center are quite unexpected: The localization of the hole between Al and P contradicts electrostatic considerations. It is evidently caused by the longer Al … O distance resulting from substitution of Si by the smaller P. This longer distance also explains why this center is still observable by EPR at room temperature in contrast to the unperturbed Al … O− (smoky quartz) center. It also has an unexpectedly high thermal stability compared to aluminum-related hole centers with nearby positive ions. All the phosphorus present is obviously associated with aluminum, in agreement with estimates of the equilibrium distribution based on a purely Coulomb attraction between Al3+ and P5+ on sites of Si4 +. The isotropic 27Al superhyperfine structure is four times smaller than in the unperturbed smoky quartz center, evidently as a result of the strong electron attraction by the pentavalent phosphorus opposite to Al which also gives rise to a large and practically isotropic 31P doublet superhyperfine splitting.

Electric dipole echoes in smoky quartz at very low temperatures

Coherent electric echo magnitudes and decay rates have been studied in gamma-irradiated natural quartz crystals in the 5–25 mK range at a frequency of 360 MHz. The echo experiments indicate the presence of two kinds of paraelectric centers. The dynamics of the two-level systems associated with aluminum centers is discussed. The tunneling centers possess rather long phase memory timeT 2 in the millikelvin temperature range (T 2 ∼10−5 sec at 10 mK) andT 2 is inversely proportional to the temperature.T 2 originates from dipolar interactions between the paraelectric centers, and spectral diffusion governs the decay of both the spontaneous and the stimulated echo.

Electrical conductivity of synthetic and natural quartz crystals

Electrical conductivity of α quartz is ionic, the current being carried by alkali ions (M+) moving in channels parallel to the c axis. A study was made of conductivity σ of one natural and three synthetic crystals in order to better understand these ionic defects. ac measurements were made over a wide range of frequencies, and complex-impedance analysis was used to separate out the bulk conductivity from electrode effects. The activation energy E for the synthetic crystals was always close to 1.36 eV and the pre-exponential A was in the range of 106 K/Ω cm. A decrease in σ resulted from electrodiffusion (sweeping) in hydrogen. For the as-received natural crystal, the value of E was 0.82 eV, but this E value increased appreciably after hydrogen sweeping or after irradiation plus high-temperature anneal. The principal observations could not be interpreted in terms of the conventional theory in which the Al3+-M+ pair and its dissociation products are the only defects involved. A modified theory, in which additional unassociated Al is present as compensation either for H+ or for oxygen vacancies, allows a detailed interpretation of the results. Supporting data are also obtained from infrared measurements.

人工水晶の着色について

Coloured crystals of quartz of gemstone-grade, citrine, amethyst and blue quartz, have been synthesized under hydrothermal conditions ranging 320-330°C and 1000-1500kg/cm2. Conditions for colourations were Fe impurity, K2CO3 mineralizer, Ag-lined autoclave for citrine and amethyst, and Co and Al impurities, NaOH mineralizer for blue quartz. These impurities were added in the forms of metals or metallic oxides. Gamma irradiation was necessary for the final colouration of amethyst. Infrared examinations of natural and synthetic quartz crystals were made in the spectral range 2000-4000 cm-1.

Dielectric relaxation phenomena in smoky quartz at very low temperatures

Audiofrequency dielectric measurements down to 4 mK on gamma-irradiated natural quartz crystals revealed the existence of anomalous dielectric behaviour. The results show a dielectric relaxation time which decreases with decreasing temperature and suggest a new relaxation mechanism in smoky quartz.

Etude des défauts des croissance dans des monocristaux naturels de quartz

Defects are studied in natural quartz crystals by X-ray diffraction topography with a Lang camera. Dislocations, precipitates and band growths revealed by X-ray studies are also characterized by other methods such as optical microscopy and thermoluminescence. Finally, a model of growth is proposed.

Thermoluminescence and thermally stimulated conductivity in quartz induced by thermal treatment after X-irradiation

Abstract Changes in thermoluminescence (TL) sensitivity and thermally stimulated conductivity (TSC) of natural quartz crystals induced by X-ray irradiation have been studied by utilizing a bleaching procedure. The magnitude of the temperature shift between the TL and TSC peaks at about 330 K depends on the thermal treatment of the sample. The experimental results can be explained by a phenomenological concept based upon a simple kinetic model. This model predicts that the density of free recombination centres in a preirradiated sample will be increased by thermal activation. This prediction is in good agreement with the predose model proposed earlier.15

Short-time-scale specific heat experiments on smoky quartz

Short-time-scale specific heat measurements have been performed on gamma irradiated natural quartz crystals in the millisecond time-scale at liquid helium temperatures. Evidence for a reduction of the specific heat has been observed in this time-scale between 1.4 K and 4.2 K.

Distinction between topography of prism faces of natural and cultured quartz crystals

AbstractResults of detailed microtopographical studies on prism faces of a large number of natural and hydrothermally grown quartz crystals are described, illustrated and discussed. In the light of these results distinction between prism faces of the two varieties of quartz is assessed. Horizontal striations, parallelogram shaped and low angle tetrahedral growth pyramids are reported as characteristic features on prism faces of natural quartz crystals, whereas hexagonal and square shaped pyramids are shown to be characteristic features on prism faces of cultured quartz crystals. Evidence of independent growth on prism faces of both the varieties of quartz crystals are given. A wide variety of growth forms, like oriented snail shaped hillocks, pentagonal elevations, rectangular spiral patterns, screw ledges, missile‐like structures, influence of impurities on advancing growth fronts, microdiscs patterns and etch patterns due to chemical etching are explained.

Growth of quartz crystals twinned after Japan Law

The flattened or elongated morphology often observed in contact twinned crystals has been referred to the so-called re-entrant corner effect at twin junctions. To re-investigate the validity of this mechanism, natural quartz crystals twinned after Japan Law have been subjected to re-growth in a commercial synthetic quartz autoclave, and the change in their morphology and surface microtopography by re-growth studied. It is found that although twin re-entrant corners may play a role of preferential growth sites, this role can be weakened considerably and in fact can become almost negligible when crystals grow under high supersaturation condition. Preferential growth at the re-entrant corner of a twin junction is probably due to clusters of dislocations concentrated in the composition plane, and not due to the so-called re-entrant corner effect in its original sense.

On the coexistence of phases at the α–β transition in quartz

AbstractThe character of the α–β transition in crystals of natural and synthetic quartz has been studied by measuring the refractive index. The coexistence of two different crystallographic modifications over some temperature range has been established. The α–β phase transition is supposed to be attributed to the near‐critical phase transitions. In synthetic quartz with Al and Fe structural impurity the α–β transition consists of two successive transitions. First the transition from the α‐phase to an intermediate one takes place, then the intermediate phase is transformed into the β‐Phase. Within a certain temperature range there exists only the intermediate phase.

ChemInform Abstract: ON THE FINE STRUCTURE IN THE INFRARED SPECTRA OF CLEAR NATURAL QUARTZ, AMETHYST, CITRINE AND SYNTHETIC QUARTZ CRYSTALS IN THE 3400 CM‐1 REGION

Chemischer InformationsdienstVolume 9, Issue 22 Physical Inorganic Chemistry ChemInform Abstract: ON THE FINE STRUCTURE IN THE INFRARED SPECTRA OF CLEAR NATURAL QUARTZ, AMETHYST, CITRINE AND SYNTHETIC QUARTZ CRYSTALS IN THE 3400 CM-1 REGION D. CHAKRABORTY, D. CHAKRABORTYSearch for more papers by this authorG. LEHMANN, G. LEHMANNSearch for more papers by this author D. CHAKRABORTY, D. CHAKRABORTYSearch for more papers by this authorG. LEHMANN, G. LEHMANNSearch for more papers by this author First published: May 30, 1978 https://doi.org/10.1002/chin.197822004AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume9, Issue22May 30, 1978 RelatedInformation

On the Fine Structure in the Infrared Spectra of Clear Natural Quartz, Amethyst, Citrine and Synthetic Quartz Crystals in the 3400 cm-1 Region

Abstract The fractional intensities of different infrared vibration bands due to hydrogen impurities have been studied in clear natural quartz, amethyst, citrine and synthetic quartz. Integral absorptions of the different bands were found to increase linearly with total hydrogen concentration. The differences in intensity ratios for some prominent bands are distinctive for the type of quartz in some cases. The ratios of isotropic to anisotropic absorption from hydrogen impurities were found to increase with total hydrogen concentration.

Fission fragment track registration and development efficiencies of some commonly used crystalline track detectors

Experiments have been carried out to determine fission fragment track registration and development efficiencies of natural quartz, mica and feldspar crystals in 2π geometry. Particular attention has been paid to the effect of different etchants and the etching conditions on various crystallographic planes. The results indicate that different crystallographic planes in natural quartz and feldspar crystals show varying degrees of anisotropy in the angular distribution of etched tracks. In general, (a) the registration efficiencies at first improve with increasing etching time and then become almost constant, and (b) boiling solutions of NaOH produce more isotropic distributions than HF. Attempts have been made to explain the above mentioned anisotropy on the basis of differences in v g and v t along different crystallographic planes.

High frequency ultrasonic relaxations in smoky quartz

Pulse-echo ultrahigh frequency ultrasonic measurements in gamma irradiated natural brazilian X-cut quartz crystals reveal the existence of Debye relaxation peaks at low (18 K) and high (155 and 255 K) temperatures which can be attributed to transitions of the hole trapped at the oxygen ion nearest to the substitutional aluminum impurities. The observed activation energies are in agreement with previous anelastic and dielectric loss measurements but the relaxation times are found to be respectively one to two, and five orders of magnitude smaller for the high and low temperatures peaks. The low-temperature peak shows an apparent radiation annealing for gamma doses in excess of one megarad attributed to the closing of tunnelling transitions of the hole from low-lying intermediate energy levels due to electrostatic shifts of the asymmetry of the double-well potential by ionized defects. Uncoupling of the sound waves to the split ground state levels of the hole may be due to the anisotropy of the deformation potential constant.

Applications of cathodoluminescence in mineralogy

Cathodoluminescence microscopy and cathodoluminescence spectrometry with the electron microprobe and the scanning electron microscope are applied to the study of some natural cassiterite, quartz and sphalerite crystals. Some examples of localization and distribution of crystalline defects revealed by cathodoluminescence microscopy are given. X-ray spectrometry and secondary ion mass analysis allow to illustrate the coincidence between the spatial variations of cathodoluminescence emission and the distribution of impurities within minerals. In order to establish a relationship between the spectral distribution of the luminescence and the nature of trace elements, comparisons are made between cathodoluminescence properties of natural and artificial zinc sulphide crystals. Particular attention is given to specimen containing copper-gallium impurities. It has been possible to distinguish between the impurities which can be responsible for the luminescence and those which are not associated with cathodoluminescence emission characteristic of the crystals. The study of cathodoluminescence intensity according to the excitation conditions led to consider the contribution of the X-ray photons generated in the specimen for the production of luminescence photons. An in-depth distribution law of generated photons similar to that used to take account of X-ray emission led to introduce an absorption function in the relation giving the measured intensity of cathodoluminescence according to the incident energy and the electron beam density.

Determination of impurities of sodium, gallium, bromine, chromium, and antimony in colored crystals of natural quartz by an instrumental activation method

Determination of impurities of sodium, gallium, bromine, chromium, and antimony in colored crystals of natural quartz by an instrumental activation method